The present invention relates to an electronic camera, and in particular to a technique to adjust a color tone under different light sources.
In a conventional camera, techniques relating to the present invention are listed below and explained.
(1) Japanese Patent Application Open to Public Inspection Publication No. 59-183590 discloses a technique to memorize white balance information for each sheet of photographed image frames and to convert a color tone based on the memorized white balance information at the time of reproducing images.
(2) Japanese Utility Model Application Open to Public Inspection Publication No. 58-161371 discloses a technique to mount a standard white plate on a back side of a lens cap and to adjust white balance by using the standard white plate.
(3) Japanese Utility Model Application Open to Public Inspection Publication No. 2-140540 discloses a technique to make color filters for adjusting white balance in a structure capable of using three colors simultaneously so that white balance adjustment can be completed for a short time period.
(4) Japanese Patent Application Open to Public Inspection Publication No. 1-305789 discloses a technique to introduce light from the outside of an electronic camera casing to color sensors through an optical fiber and to adjust white balance by using light from the optical fiber.
(5) Japanese Patent Application Open to Public Inspection Publication No. 63-267091 discloses a technique to utilize a fact that a fluorescent light source contains flicker and to adjust white balance by identifying a kind of a light source based on flicker when the flicker is detected from the light source.
(6) Japanese Patent Application Open to Public Inspection Publication No. 63-236931 discloses a technique to discriminate kind of a light source based on chromaticity coordinates in the case that a light source is a fluorescent light.
However, in the above conventional techniques, since the electronic camera is subject to color tone adjustment for photography under a light source of day light, a skin color may be photographed relatively dark under a regular type fluorescent light as an example even when white balance was adjusted, resulting in that sufficient color tone may not be obtained. Further, a problem that a red color component becomes too strong under a tungsten light source light may happen.
Further, white balance is not adjusted in accordance with human adaptability. In such a white balance adjustment, ratios among R, G and B signal values outputted from CCD are merely changed or color difference values between R and Y and between B and Y are changed. However, even if white balance is adjusted by those techniques, a color other than white, in particular, a visual impression for a memorized color of a skin color may change to cause malfunctions.
Still further, when color filters are deteriorated, spectral distribution characteristics of the color filters may deviate from normal characteristics for wavelength so that color adjustment cannot be conducted correctly. Correction for the deterioration of the color filters is conducted only once when an electronic camera is assembled, and after the camera is delivered as a product, correction cannot be conducted. Accordingly, color balance becomes out of order due to deterioration as time elapses, with the result being in that good color tone cannot be obtained.
Furthermore, although adaptability of the human eye is well known according to the Von Kries model, there has not yet been a technique to utilize it for a image photographing system.